1. Field of the Invention
This invention relates to a dielectric heating apparatus comprising a pair of opposed electrodes, at least one of which is provided with a heating means for the prevention of condensation.
2. Related Art Statement
Heretofore, dielectric heating apparatuses have been utilized for drying moisture-containing articles such as green ceramic products and the like as disclosed, for example, in Japanese Patent Application Publication No. 59-8,955.
In this case, as shown in FIG. 4, a pair of opposed flat plate electrodes 2 and 3 are arranged in parallel with each other so as to sandwich a belt of a belt conveyor 1 therebetween at proper intervals, and a high frequency voltage is applied across the electrodes 2 and 3 to conduct dielectric heating of articles 4 to be dried on the belt, whereby water contained in the article 4 is evaporated therefrom. A numeral 5 represents a duct for discharging vapor generated from the article.
However, when the article containing a large amount of water is subjected to the dielectric heating as mentioned above, vapor generated from the article is frequently cooled by contacting with the surfaces of the upper and lower electrodes to cause condensation at the electrode surface. Particularly, water droplets which condense on the upper electrode hang down therefrom, and consequently a concentration of electric field often occurs between the droplet and the article to cause electric discharge. By such an electric discharge, the article may be burnt or damaged.
In order to prevent the above mentioned condensation at the electrode surface, there have hitherto been proposed countermeasures, including a heater element of nichrome wire being embedded in the electrode, hot air being blown from the outside to the electrode, a hygroscopic porous plate being mounted onto the electrode, and so on. However, in the first countermeasure, the complete area of the electrode can not uniformly be heated, and also the disconnection of the nichrome wire is apt to result. In the second countermeasure, the article to be dried is heated in addition to the electrode, so that the article can not be dried uniformly. In the third countermeasure, the electrode must be made large-size, or the hygroscopic porous plate hangs down from the electrode in use so as not to hold a flat plate shape and peeling may result owing to the service life of the hygroscopic porous plate itself.